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USGS East Coast Earthquake Q&A

September 6, 2011

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Transcript

(Original "air" date Aug 26, 2011)

Tim Fullerton: Good morning and welcome to the U.S. Department of the Interior. My name is Tim Fullerton, I'm the director of new media here. We want to welcome you this morning for joining us about this very important chat about the East Coast earthquake that affected many of us earlier this week.

We are fortunate enough to have Dr. Mike Blanpied with us today from the U.S. Geological Survey, who serves as the associate coordinator of the USGS Earthquake Hazards program. He will be answering your questions for the next 30 minutes, so if you haven't already submitted a question you can do so in the chat box below the feed and we'll get to as many of them as we possibly can.

But first, I want to turn it over to Dr. Blanpied who will give us a brief overview of what we saw earlier this week.

Dr. Mike Blanpied: Well, thanks very much, Tim. This was really an exciting Tuesday in the DC area and throughout Virginia. We had a magnitude 5.8 earthquake in Central Virginia. It was the biggest one that any of us had experienced in the East Coast and that the East Coast had experienced in quite some time.

The shaking from that earthquake, as is typical for Eastern U.S. earthquakes, went very far. People were shaken and detected the earthquake all the way up to Maine, to Florida, Ontario and west at least as far as Missouri, very widely felt earthquake, perhaps the most number of people feeling an earthquake in the United States since the country's beginning.

We were very fortunate that the earthquake struck in a relatively unpopulated area. It caused some damage from place to place but no deaths, and that was extremely fortunate. That earthquake, had it landed right underneath an urban area, really could have been quite damaging.

This earthquake serves as a warning to us that earthquakes are not just a West Coast problem, they're a national problem. And it's sort of a wake up call that while we know we need to be prepared for hurricanes and winter storms and so forth, earthquakes are another hazard that face us in this Central and Eastern US, and we can be ready for those as well.

And there are some simple steps to prepare, make sure your family, your business and yourself are prepared to react if an earthquake does strike, and to make sure that you ride it out safely, and that if services are disrupted and so forth that you're OK in the days afterwards. And we can talk about those things if there are questions on those subjects later on.

Tim: Great. Well, let's jump into the first question. This one came in from the live chat a few seconds ago. The question is: "How often do earthquakes hit the East Coast?"

Dr. Mike: Well, not nearly as often as in the West Coast, of course. We have the perception that earthquakes are really a West Coast issue. In fact, earthquakes strike every state in the country, but with much more frequency in the Western U.S. than in the East, with some exceptions.

Earthquakes are really patchy in where they occur. We have a zone in Central Virginia called the Central Virgina Seismic Zone that does experience frequent small earthquakes and occasional large ones. Some of you may remember in December of 2003 there was an earthquake of about four and a half in the same area that caused quite a bit of shaking.

We have to look farther back, back decades or centuries, to see the larger earthquakes throughout the Eastern U.S. and Eastern Canada. There have been earthquakes as large as in the low sevens that have caused in some cases quite a bit of damage, and were they to happen today, would cause more damage.

So, we do get earthquakes from time to time, not with the frequency of Los Angeles, or San Francisco or Seattle, but from time to time.

Tim: Great. Well speaking of San Francisco, we have a question from Larry out there who probably has a lot more experience with earthquakes than some of us who have felt the one on Tuesday, and his question is, "Are there major fault lines in Virginia as there are in California like the San Andreas Fault, or is Virginia on a larger, flat tectonic plat with no fault lines?"

Dr. Mike: Well, there certainly are fault lines. We're in the middle of a tectonic plate here. The boundaries of that on the West are the San Andreas and the Cascadia Subduction Zone running up the Pacific Northwest, and on the East the edge of the tectonic plate actually runs down the middle of the Atlantic Ocean. So we're sitting in the middle which is a relatively stable part of a tectonic plate.

The rocks here are old and cold but they preserve in them the faults that were part of the processes that led to the formation of the continent hundreds of millions of years ago. So there are lots of faults available to have earthquakes and there are stresses bearing on those faults, but in very few cases can we identify a particular major fault zone that is likely to have a big earthquake.

It's more kind of a smattering of earthquakes on fault zones, and in some cases we don't really even know which fault it was that had the earthquake. That's the case for Tuesday's magnitude five.

Tim: Great, thank you. We have a question from Rhonda in Colorado asking about the earthquake that happened out there a few days before. "Hours prior to the East Coast earthquake there was one in Southeast Colorado, and her question is were these two related?"

Dr. Mike: Probably not. We do know that earthquakes can talk to each other. Aftershocks are a manifestation of that. If you have a big earthquake, it causes stresses and other influences on the faults in the immediate vicinity, and that leads to aftershocks. Very large earthquakes can be observed to cause earthquakes to light up quite a distance away.

But in terms of a magnitude five, we really don't think that magnitude five or six earthquakes can communicate over those sorts of distances. So it's most likely just happenstance that the two of them occurred that close together in time.

Tim: Great. We're going to move to a preparedness question because many of us, including all of us in this building, felt the earthquake on Tuesday, but many of us are not used to that experience. And so one question that came in from Rose in Washington, D.C. was, "Is it safer to stay put, or go in the basement or go outside during an earthquake?"

Dr. Mike: During an earthquake you generally have very little time to actually react. The best thing to do is to be prepared to take the right action immediately. If you're indoors, get underneath a heavy piece of furniture. Drop down, cover you head in case there are falling objects and hold on. Drop, cover and hold on.

If you're already outside, then move away from buildings where there might be falling objects coming off the buildings, pieces of brick or whatever that could hurt you. If you're very near a building and you could duck into a doorway, that might be a safe way to do it. What you don't want to do is to rush from inside the building to outside, because in fact, one of the least safe places is directly outside the building where things could be falling.

If you're in your car, bring the car calmly and safely to a stop. The car is actually a fairly safe place to be unless you run into somebody, so that's fine.

So just take some calm actions to protect yourself. And the biggest hazard really for buildings in this country is falling objects, and so protect your head.

Tim: Great. We were talking off camera a moment ago about a lot of people were thinking that doorways were the safest place if you're in a building, but what you're saying is actually to get under a desk or get under some heavy furniture is a better idea than standing in a doorway.

Dr. Mike: That's right. In older generations of construction when we were building houses of rocks say, there would be a heavy beam that would be part of the integral construction of the building that would make doorways a very safe place to be. In modern construction, doorways are not a particularly safe place, plus you've got the problem of the swinging door. So really it's better to get yourself under furniture if you can rather than rush to the doorway.

Tim: Great, thank you. We got a lot of questions about hydraulic fracking. The question that was coming in the most was do you see any connection between earthquakes and the process of fracking for natural gas extraction?

Dr. Mike: Well, we know that the fracking process, that's where we're inducing fractures into rock within a well in order to increase the ability to extract things from the rock. That process can cause very small earthquakes but the fracking process doesn't really, we don't think, induce large earthquakes.

The thing that can induce large earthquakes is the high pressure fluid injection, waste fluid injection, that's done in some places. However, as far as we're aware there's not really the mining or the fluid injection processes going on in Virginia that would have connected this earthquake with anything like that. And just to be clear, the connection between fracking and fluid injection and earthquakes is an area of active research and really we're only starting to learn about how those things are connected.

Tim: Great, thank you. We're going to move to another question from Linda in Tennessee which is a four part question, so I'll try to get through this.

Dr. Mike: OK.

Tim: One was, "What fault caused this quake? Do we know approximately when this fault was last activated? And actually we're just going to go into the third part but if so, what time frame estimate is available for more activity on this fault?"

Dr. Mike: Right. The Central Virginia Seismic Zone is characterized by sort of a diffuse area of seismicity of earthquakes. Those earthquakes don't appear to line up along a particular line that we would identify as an active fault. It's more that there's high stresses in the rocks - and we can talk about why if you're interested - that cause earthquakes probably on numerous faults at various places of depth.

The 5.8 earthquake did not come to the surface and cause rupture at the surface such as on the San Andreas Fault when there is a big earthquake. It was buried. We don't really know which faults are there and we may never know which fault this earthquake happened on.

What we can do given that absence of knowledge is to look more generally at the rate of earthquakes that occur, and we know that earthquakes of magnitude four happen on this several decade scale, magnitude fives more rarely. We've had two in Virginia in 100 years or a little more.

And then we can use that information about the frequency of earthquakes to then say what the hazard is, that the hazard from shaking, and it's that kind of information about how likely it is that the ground is going to shake regardless of where the earthquakes actually came from, it's that information about shaking that can give us the building code provisions that allow us to make safe structures. And really, that's the key.

Earthquakes can come and go and if we have nice, safe structures and we're ready to ride out the earthquakes, and if the electricity goes out we're ready to deal with that, then earthquakes really aren't a problem.

Tim: Great, thanks. This is probably a good point to just welcome the people who are joining us now. If you've missed the first 10 or 12 minutes of this chat, it will be available on doi.gov next week. And also, if you're looking for more earthquake information, the USGS has a great section of their website at earthquake.usgs.gov. There's a lot of information there, so if you get a chance, you should definitely check that out.

Dr. Mike: One of the interesting features on the website for those of you who felt the earthquake is a feature called "Did You Feel It?" If you go to the USGS website or earthquake.usgs.gov, for any particular earthquake that's a large earthquake there, you can actually fill out a short form that contributes your experience from the earthquake, and that helps us build a map that shows the distribution of shaking.

There's a beautiful map for this Virginia earthquake, because about 135,000 people have contributed all over the Eastern U.S. and Southern Canada. It very beautifully shows the distribution of shaking from place to place. And that's of scientific use as well so we appreciate your contributions.

Tim: That's great. The next question as we move on is from Adnan who wanted to ask, "What is the maximum intensity of an earthquake that could hit the East Coast?"

Dr. Mike: Well, we can't really say what the maximum is. We can look at experience over the last few hundred years, and the biggest earthquakes that have struck have been in the low sevens.

There was an earthquake off the Grand Banks south of Newfoundland back in 1929 that was estimated to be about a magnitude 7.2. There was an earthquake in Charleston, South Carolina in 1886 that did quite a bit of damage that was somewhere in the low 7's, seven to 7.2, 7.3. And so we know that earthquakes of that size are capable of happening and so we build that into our understanding about the likelihood of shaking.

Another place in the Central U.S. that we know is capable of large earthquakes is the New Madrid Seismic Zone that runs between Missouri, Tennessee, Kentucky and that area, where back in 1811, 1812 there were a series of very large earthquakes that we estimate to have been at least magnitude 7.

And the largest of those, which was probably in the mid 7's, 7.3, 7.5, something like that again caused very widespread, even heavier shaking than we experienced on Tuesday and actually caused quite a bit of shaking all the way to the East Coast in the Washington area.

Tim: Great. All right, well we're going to move to another question that's specific to DC.

Dr. Mike: OK.

Tim: You can definitely see there's a lot of interest on the East Coast about this.

Dr. Mike: Sure.

Tim: Linda in the District is asking, "Did last year's DC earthquake, which was around a magnitude 3.4 on July 16th, and coupled with this earthquake, that was a 5.8, does that say anything about an earthquake happening in the summer of 2012?"

Dr. Mike: No, not particularly. We know that the actual greater DC area is relatively quiet, seismically. That magnitude three and a half or so earthquake was the largest one that had been recorded in this area. And it caused shaking over a fairly widespread part of the DC area and a lot of people felt it. But that's at a fair distance from the central Virginia seismic zone, which is in a much more active area of earthquakes.

And there's probably not really much communication between the two. And the fact that we occasionally have earthquakes here and we, a little more occasionally, have earthquakes there, doesn't indicate that we're on the ramp to anything in particular coming up in the next summer or even in the next longer period of time.

Tim: Great. Thanks. Another question, this is from Sally. Again, DC related. "Is the DC metro area close to the Appalachian fault? And if so, why has there been a long gap between seismic movements? Should the Appalachian region be expecting more activity in the near future?"

Dr. Mike: Well, there are parts of the Appalachians that are quite seismically active. Southwestern Virginia, there's actually a zone of Eastern Tennessee that is quite active, the Eastern Tennessee seismic zone. And again, these are places that have large amounts of stress left over from the plate tectonic process.

There's additional stresses that have actually been added due to the process of glaciers advancing down over the northern part of the United States and then retreating. That weight of that ice load has actually, probably, caused amounts of stress that are being relaxed and causing changes in the stressing on faults and so forth. That's, again, an area where we're trying to get a better understanding of how those stresses work.

So, yeah, the best thing to do is really to look at the history of earthquakes. And, again, the USGS is a source of maps like that for every state, or for every region, we have maps showing the historic seismicity. And also, our understanding about the shaking hazard related to potential future earthquakes. So, people can take a look at that.

Tim: Great, thanks. The next question is from Jake, who asked it on the chat here. And his question is, "How come this quake was felt all the way in Chicago but the one in Colorado, earlier in the week, wasn't felt quite as far?"

Dr. Mike: Yeah, that's a great question. Yeah, Central and Eastern US earthquakes really are interesting beasts. Once you get to the Rockies west, the continent is younger. There's more active processes going on related to the building of the Rockies, and of course, the very active plate tectonics farther west. Those rocks are younger and warmer and more chewed up than the rocks in the Eastern US.

If you have an earthquake in the East, the rocks are old and cold, and seismic energy, seismic waves caused by that earthquake travel very far through those old cold rocks. And so, they can spread all over the Eastern US.

If you have a magnitude 5.8 in Nevada or California or Western Colorado, the felt area will be much more compact. So, the difference between this and the Colorado earthquake, one is, the Colorado earthquake was much smaller. And it was in a younger geology, so it just isn't felt as far.

Tim: Great. Thank you. The next question is coming in from the chat as well, and actually, we've had a few people ask this. And they were asking about, "Are there any known faults that go through the Manhattan region?"

Dr. Mike: Yeah. Yeah, New York has a hazard that the whole New England area does. Again, they are all older fault zones that are remnant there, and occasionally there are earthquakes. There have been earthquakes large enough to cause some pretty heavy shaking in the New York area. Back in 1944, there was a magnitude high 5s, magnitude 5.8 earthquake that shook near the New York region. Particular faults have been mapped, and there are probably other faults that we don't know about.

And so, but we do have a concern for our eastern cities that have an older set of buildings that are not built for modern seismic safety. Even, as we've said, a magnitude five earthquake that occurs in rural Virginia, we got a pass on that. If a magnitude five point earthquake occurred near Manhattan, near Boston, we could have a problem.

And this is a question from Tom, who is out in Minnesota. And he's saying, "I'm very concerned by the lack of public understanding of what to do when an earthquake hits. Not so much in areas where preparation training and public understanding exist, but in areas like DC or even in areas such as rural Minnesota," where Tom is from. "The image on TV suggests the opposite of drop, cover, and hold on. What can we do to increase public understanding of what to do in the event of an earthquake?"

Dr. Mike: Well, I think one thing to do is just to use the earthquakes that do occur as reminders to get prepared. There are sources of information from USGS, go to earthquake.usgs.gov/prepare. There's information there and links to others. The FEMA website has a lot of good information, the Red Cross website has a lot of good information.

In preparing in advance for earthquakes, you actually take many of the same steps as you do for preparing for other hazards, hurricanes, ice storms, electrical outages, tornadoes, if they're in your area, and so forth. It's having a plan and having supplies.

Having a set of supplies on hand, where you've got food, water, maybe a camp stove. Some people have a generator. Medicines, if you have prescription medicines. Kids' toys, you know, whatever it is going to take so that your family or your business place can be comfortable and just sort of ride it out in the days after, if a hurricane comes through, or an earthquake knocks out the electrical grid, or whatever.

And then, the other thing is to have a plan. The worst feeling is to have an earthquake knock out the communication system, and you don't know who's supposed to go to the school and pick up the kids or where you're supposed to meet. So, having an idea ahead of time, just, OK, you're going to go there, I'm going to go there, we're going to call Aunt Susie. Just have that kind of worked out so that you know what you're going to do.

And for businesses, have a plan for what's the response of the employees going to be, how are you going to communicate with the workforce? Should they come to the office? Should they not? And so forth. Having that all worked down in advance will not only make it a more comfortable situation, but it'll also provide a lot more comfort to people at a time when things are very confusing.

Tim: What I think I would just add to that, if you have further questions that are more specific that you would like to ask about preparedness, you can follow the USGS on @usgs on Twitter. You can also "Like" them on Facebook. And we try to answer as many of those questions on there. So, if you have any questions, or have friends and family that have questions that they'd like to have asked, please follow those two social networks and we will do our best to answer as many of them as possible.

Dr. Mike: And we can post some on the Facebook page, or we can post some links. And also, in that /prepare page at usgs, there are some links to get some good information.

Tim: Well, we've got time, probably, for a couple more questions. So, if you've got a really burning question you'd like to ask Mike, please post it now, because we're going to probably stop at 11:30, because we've heard that President Obama is going to be speaking on Hurricane Irene.

We see that there's some questions coming in here. So, if you're interested in hearing the President speak, go to whitehouse.gov/live and you'll be able to watch it there at 11:30. But until then, we'll answer as many questions as we possibly can.

So, the next one comes from Tony from the chat. And he was asking, he heard that this earthquake was on a reverse fault line. And he wanted an explanation of what that was, or if that is even something that exists.

Dr. Mike: It does exist, and it's more of a scientific interest, but there's basically three ways that faults exist in the ground and that earthquakes occur on them. If we've got, if my hands are the two sides of the fault, if the fault goes more or less up and down and the sliding is sideways, we call that a strike slip fault. The San Andreas has strike slip earthquakes, that's the very familiar example.

If the fault is tipped over and one side goes up, so, you're pressing the fault together and one goes up over the other, that's called a reverse fault, or a reverse faulting earthquake. And that's what happened in Virginia. And that's typical that we know that there's east/west compression across most of the United States due to the plate tectonic forces. And so, faults that are inclined like that will tend to slip in this manner.

The other third case is where you've got a pulling apart motion, and then, again, that incline fault will slide this way. And, for some reason, geologists have called that a normal fault. We don't know why they're normal, more normal than the other kinds. But those are normal.

Tim: Great. All right. Now we're going to go to a question from Zack in Virginia. And he's asking, "How long will the aftershocks continue in Virginia?"

Dr. Mike: Good question. Almost every large earthquake causes aftershocks. And aftershocks are a manifestation of the stresses that have changed in the faults around. And those aftershocks are generally concentrated in the general area, though you can have some at larger distances.

What we know about aftershocks is that their rate falls off in a very, kind of, predictable way with time. We can't predict the time and location and magnitude of any particular aftershock, nor can we of any earthquake. However, we can say that the likelihood of aftershocks is the highest at the beginning and then falls off with time.

Now, aftershock sequences can go on for weeks, months or even years. And those aftershocks can be large. We may still have more aftershocks of magnitude four size. We may have a magnitude five aftershock. It's hard to say. The likelihood of that falls off with time.

But the key thing is, just to be aware, as the earthquake reminded us, that earthquakes are an eastern feature, the earthquake reminds us that we may be feeling aftershocks. And so, again, just be prepared. If you feel the shaking, protect yourself, ride it out, and then move on.

Tim: Great. All right. The next question has come from Heather. And she is asking, "Are earthquakes on the East Coast related to continental drift, and when it drifts causing old fault lines to reactivate?"

Dr. Mike: In a general sense, that's right. Continental drift is now generally referred to as plate tectonics, the idea that the Earth's surface is divided into large plates that move relative to each other. Now, as I said, we're in the middle of a tectonic plate here, but we have the forces that are acting around the edges from the other tectonic plates. And so, to some extent, those forces are keeping compression on the faults in the interior of the plate, and leading to earthquakes.

Tim: Great. And we've obviously got a lot of interest on Hurricane Irene. And T.J. in Virginia is asking, "Is there any relation of the earthquake to the hurricane?"

Dr. Mike: Only in that they are both hazards for which we need to be aware. But there's really no connection between atmospheric phenomenon and hazards and earthquakes under the ground.

Tim: Great. Great. And we have a question from Sal Marie here on the chat. "Is there any published research that you can recommend for people to read to better understand seismic activity?"

Dr. Mike: Well, there's just lots and lots of activity and material to read. One place to start, there are many places you could start, just start with web searches. Or search in the library. But one place to start is earthquake.usgs.gov. We have a tab there about learning.

And so, you go there and there's lot of information and links to sources, questions and answers, FAQs and so forth. I encourage you to start there. If you do have particular questions, you're not able to find the answers, post the questions and we'll try to get those answers to you.

Tim: OK. Well, we have time for one final question. We want to thank everyone for joining us. But the final one, and this one came in from Kathy on Facebook. She wants to know what makes that sound she heard during the earthquake.

Dr. Mike: Yeah, earthquakes do make sound, and that's one of the characteristic things. Now, if you're in a building, you may hear creaking, groaning, squeaking, things like that, rumbling. Those are generally due to the building itself. Buildings groan and creak because all these little parts are sliding around, things may be moving. So, usually, what people hear is building sounds.

However, people have heard earthquake sounds outside, and that seems to have to do with the groaning of the ground. It's just, you're shaking the ground very hard and parts of it are moving around. So there actually are earthquake sounds, just due to the motion of the ground.

Tim: Great. Well, all right, that's all the time we have for today. I want to thank Dr. Blanpied for joining us and answering all of your questions, they were really, really good questions. If there are more that you would like to have answered you can go to the USGS Facebook page where you can follow USGS on Twitter @usgs, and they will answer as many of them as possible.

And as we've mentioned a few times, you can go to earthquake.usgs.gov. If you're joining us late, the full video of this will be available on doi.gov early next week. And we just want to remind you that in the next few minutes, President Obama will be talking about Hurricane Irene at whitehouse.gov/live. So again, thank you very much for joining us.